In general, a fuel cell generates water and electricity using hydrogen and oxygen. The principle of operation of the fuel cell is that electrons are generated when hydrogen is ionized by the anode and the generated electrons move to the cathode through an electrolyte in the middle. Electrical energy is generated in a process of the electrons moving. A reaction in which water is generated by a reaction of hydrogen and air is an exothermic reaction, and heat and water can be obtained through such a reaction in addition to the electrical energy.
In contrast, a reformed hydrogen compound is used as the fuel of a fuel cell because it is difficult to obtain hydrogen itself that is used as the fuel of a fuel cell. That is, fossil fuel, that is, a compound of carbon and hydrogen, is used as the fuel of a fuel cell.